Bath for the electrodepositing of cobalt



Patented a.- 15, 1935 ES PATE INT" orrice BATH FOR THE ELECTRODEPOSITING 0F COBALT Henri Berger, Paris, France No Drawing. Application June 7, 1934; Serial No. 729,418. In France October 3, 1938 40laims.

Various solutions have been proposed up to the present time for-electroplating metals and cobalt, either with a view to hardening the surface of the metal (cobalting of printing plates), or in order to obtain surfaces having a maximum reflecting power (cobalting of metallic mirrors and reilectors), or merely in order to decorate. the metal that is treated by the electrodepositing process or to protect it against oxidation.

All the electrolytes that have been utilized up ,to this time consisted chiefly of ordinary cobalt sulfate or of ammoniacal cobalt sulfate, with or without the addition of earth or alkali-earth metals, these additions being intended to increase to promote anodic corrosion.

The drawbacks of such solutions are that they can be utilized only with limited current densities and, especially, that they only permit the use of low tensions, under which conditions it is possible to obtain only blackish deposits, either granular or little adhesive, which most often necessitate a preliminary coppering or brassing when the electrodepositing is to be effected on iron or steel.

It has already been suggested to utilize as electrolyte a solution containing chiefly cobalt chloride. But up to now such solutions have yielded only defective cobalt deposits, even with the addition of earth or alkali-earth metal salts, gen erally employed for improving them. The percentage of metal in such baths rapidly decreases due to anodic polarization and there results an irregular working, which makes it necessary to frequently add cobalt chloride.

The object of the present invention is to provide an electrolytic bath which does away with these drawbacks.

To this effect, the electrolyte that is utilized consists chiefly of cobalt chloride CoClzfiHzO, but according to the present invention, there is added to the solution an alkaline bifluoride with, eventually, boric acid. The latter is intended to serve to maintain a normal acidity of the bath.

In such baths, the anodic corrosion is per- I fectly regular, which maintains the metallic perthe conductibility or the power of penetration or centage at its normal value, so that the operation is very regular and very easy to control.

Example a An aqueous solution containing from to 600 grammes of cobalt chloride per litre and from 10 to grammes of ammonium bifluoride makes it possible to obtain very white cobalt deposits, which are perfectly adhesive, even when made directly on iron and steel and which can be brightly polished, the conditions of the operation'being very much facilitated from the point of view of the current regulation.

As a matter of fact, experiments proved that, with a tension which may vary between 2 and 6 volts and a' density of current ranging'between 2 and 15 amperes per square decimetre, with a normal interval between the electrodes,'the de-' posit has a fine grain and is evenly white, very smooth and very supple; By raising the temperature of the bath, these figures are substantially increased, as in the case of nickel-plating.

The addition of boric acid'to the bath above mentioned gives still better results. I may also, according to the invention, add to the electrolyte in question various products intended to give brightness to the deposit (colloids), or to avoid pitting (nitrates), in the usual proportions, these products being well known in the art of electrodepositing.

While I have described what I deem to be a practical example of the present invention, 'it should be. well understood that I do not wish to be limitedthereto as there might be changes made therein-without departing from the principle of my invention as comprehended within the scope of the appended claims.

What I claim is:

1. A bath for the electro-depositing of cobalt containing cobalt chloride mixed with an alkaline bifluoride.

2. A bath for the electro-depositing of cobalt 40 containing cobalt chloride mixed with an alkaline bifluoride and boric acid.

3. A bath for the electro-depositing of cobalt which contains from 50 to 600'grammes of cobalt U chloride and from 10 to 200 grammes ofkaline bifluoride per litre of water.

4. A bath according to claim 3 in which the alkaline bifluoride is ammonium bifluoride.

HENRI BERGER. 

